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Update behaviour of mstatus.mpp and mprv on mret to match priv-1.12 spec

This commit is contained in:
Luke Wren 2022-05-26 00:42:50 +01:00
parent a17b941e38
commit 156fbcd019
1 changed files with 12 additions and 0 deletions
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12
hdl/hazard3_csr.v
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@ -158,6 +158,14 @@ reg mstatus_tw;
wire wen_m_mode = wen && (m_mode || debug_mode);
// Spec text from priv-1.12:
// "An MRET or SRET instruction is used to return from a trap in M-mode or
// S-mode respectively. When executing an xRET instruction, supposing xPP
// holds the value y, xIE is set to xPIE; the privilege mode is changed to
// y; xPIE is set to 1; and xPP is set to the least-privileged supported
// mode (U if U-mode is implemented, else M). If xPP=M, xRET also sets
// MPRV=0."
always @ (posedge clk or negedge rst_n) begin
if (!rst_n) begin
m_mode <= 1'b1;
@ -173,6 +181,10 @@ always @ (posedge clk or negedge rst_n) begin
mstatus_mie <= mstatus_mpie;
if (U_MODE) begin
m_mode <= mstatus_mpp;
mstatus_mpp <= 1'b0;
if (!mstatus_mpp) begin
mstatus_mprv <= 1'b0;
end
end
end else begin
mstatus_mpie <= mstatus_mie;